Method for fabricating a laminate film, laminate film, and method for fabricating a display device

ABSTRACT

Adhesive layers are formed on the two opposing surfaces of a transparent support. At least one of the adhesive layers is made of a material of which the cured state changes by application of external force, such as a photocurable resin. A separator on the adhesive layer is peeled off, and the adhesive layer is irradiated with light. A lens sheet is then pressed against the adhesive layer. The adhesive layer is cured to a degree of hardness with which the adhesion state between lens sheet and the adhesive layer no more changes. In this way, a laminate film of the lens sheet fixed to the transparent support via the adhesive layer is obtained. The laminate film is bonded to a polarizing plate on the viewer&#39;s side of a liquid crystal display element via the other adhesive layer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for fabricating alaminate film, and in particular, relates to a method for fabricating adisplay device (e.g. liquid crystal display device) using a laminatefilm and having improved viewing angle characteristic.

[0003] 2. Description of Related Art

[0004] Liquid crystal display devices, which typify flat panel displays,have features of being lightweight, thin, and low in power consumption,compared with CRTs, and thus find applications in wide-range fields suchas OA apparatus, car-mounted TV sets, car navigation systems, andmonitors for video cameras.

[0005] A major problem relating to such liquid crystal display devicesis that the viewing angle dependence is large. The viewing angledependence refers to the following phenomenon, for example. When thescreen of a display device is viewed from a direction tilting by anangle exceeding a certain angle range, an image that should correctly bedisplayed in black appears whitish, or reversal in gray scale levels isobserved, causing reduction in display quality. From theses viewingdirections, the viewer fails to correctly recognize the display image.When the angle range within which the viewer correctly recognizesdisplay image is narrow, it is said that the viewing angle dependence islarge.

[0006] The viewing angle dependence occurs for various reasons. Theseinclude, for example, twist orientation (i.e. helical structure) ofliquid crystal molecules (the direction of a helix, the position atwhich liquid crystal molecules start forming a helix defined by therubbing direction), the refractive index anisotropy of liquid crystalmolecules (difference in retardation in the direction of propagation oflight), the characteristics of a polarizing plate (whether or not theselectivity in the light oscillating direction is good), and thedirectivity of light rays from an area light source.

[0007] In general, transmission type liquid crystal display devices aredesigned, in consideration of the viewing angle dependence describedabove, so that the position at which the display can be viewed mostnicely falls within the range in which the viewer normally views thedisplay. For example, design is made so as to enhance the contrast ratioof the center area in the screen in the direction normal to the plane ofthe screen or in a somewhat downward direction from the viewer, comparedwith the surrounding areas in the screen.

[0008] By the above construction, however, the viewing angle range isstill insufficient. In particular, liquid crystal display devices havelarge viewing angle dependence in the upward and downward directionswith respect to the screen. In order to solve this problem, variousmethods have conventionally been proposed.

[0009] For example, Japanese Laid-Open Patent Publication No. 7-43703discloses a liquid crystal display device in which a material is filledbetween a microlens array sheet and a liquid crystal display element.The material has a refractive index equal to or less than the smallerone of the refractive indices of the materials constituting themicro-lens array sheet and the liquid crystal display element.

[0010] Japanese Laid-Open Patent Publication No. 10-73808 discloses aliquid crystal display device in which a light diffusing sheet is placedon the front surface of a liquid crystal display element. The lightdiffusing sheet includes a first diffusion layer containing a lightdiffusing agent formed on a transparent member and a second diffusionlayer having concave and convex portions formed on the first diffusionlayer.

[0011] In both the above conventional techniques, the microlens arraysheet is placed on a polarizing plate constituting the liquid crystaldisplay element. The material having a refractive index which isdifferent from that of the microlense array sheet is provided betweenthe microlenses array sheet and the polarizing plate.

[0012] Japanese Laid-Open Patent Publication No. 7-120743 discloses aliquid crystal display device in which convex tip portions of amicro-lens array sheet are in close contact with the surface of a liquidcrystal display element.

[0013] Japanese Laid-Open Patent Publication No. 9-127309 discloses aliquid crystal display device in which an adhesive layer is formed onconvex tip portions of a micro-lens sheet. The ratio of the height A ofthe convex portion to the thickness B of the adhesive layer (A/B) mustbe more than 1 and equal to or less than 1000.

[0014] Japanese Laid-Open Patent Publication No. 9-194799 discloses aliquid crystal display device in which spacers are placed between arough surface and an adhesive layer.

[0015] In the above conventional techniques, the convex tip portions ofthe microlens array sheet are partly put in contact with the liquidcrystal display element via an adhesive layer, to control the proportionof the contact portion of the lens array to the non-contact portionthereof. In this way, the degrees of transmission and divergence ofoutgoing light are controlled, and thus the viewing angle characteristicis improved. In either case, the microlens array sheet is placed on theside of the liquid crystal display element closer to the viewer(viewer's side), so that light outgoing from the liquid crystal displayelement is diffused to the side on which the microlenses are formed(lens formation directions), to attain improvement in viewing anglecharacteristic.

[0016] The above conventional techniques have the following problems.

[0017] In general, a pair of polarizing plates are placed on the frontand rear surfaces of a liquid crystal display element for controllingthe polarizing state before display of images.

[0018] The polarizing plates are made of polyvinyl alcohol (PVA) andtriacetyl cellulose (TAC). PVA is impregnated with iodine, and theresultant material is drawn in one direction to align the iodinemolecules, so that light polarized along the drawn direction is absorbed(or transmitted) and thus the polarizing state of incident light can bealigned in uniform.

[0019] During the above drawing, as shown in FIGS. 22A and 22B, finewaves 222 are generated on the surface of a polarizing plate 221 alongan absorption axis (or a transmission axis) as the drawn direction. Thisis due to a miniscule variation in the thickness of the polarizing plate221 caused by the drawing. These waves do not influence the display whenthey are observed only through the polarizing plate 221. However, asshown in FIG. 23B, when a light diverging element 235 such as amicrolens array sheet is placed on a surface of a polarizing plate 231,in particular, when the light diverging element 235 is bonded to apolarizing plate 231 via an adhesive layer 234, waves 232 generated onthe surface of the polarizing plate are magnified. As a result, thedisplay quality greatly deteriorates.

[0020] The display quality also greatly deteriorates in the case ofusing a conventional double-sided adhesive tape as the adhesive layer234 for bonding with the light diffusing element 235 and the case ofusing a curable resin as the adhesive layer 234. In these cases, thecontact area between the light diffusing element 235 and the adhesivelayer 234 is partly changed due to scars formed by hitting with foreignsubstances generated in the bonding process (concave and convexdeformation caused by foreign substances) and deformation caused byexternal force (by the viewer who touches the lens surface). Thispartial change in the contact area causes generation of spot defects 233a and bar-shaped defects 233 b as shown in FIG. 23A.

[0021] No means for solving the above problems have been mentioned inthe prior art literature.

[0022] An object of the present invention is to provide a laminate filmwhich enables an optical film to bond uniformly to a surface (e.g.,surface of a display element), even if the surface has unevenness, amethod for fabricating such a laminate film, a display device using sucha laminate film, and a method for fabricating such a display device.

SUMMARY OF THE INVENTION

[0023] According to the first aspect of the present invention, a methodfor fabricating a laminate film including a transparent support havingtwo opposing surfaces and an optical film is provided. The optical filmis formed on one of the two opposing surfaces of the transparent supportvia an adhesive layer made of a material of which the cured statechanges by application of external energy. The method includes the stepsof; applying external energy to the adhesive layer; pressing the opticalfilm against the adhesive layer to stick the optical film and theadhesive layer together; and curing the adhesive layer to a degree ofhardness with which the adhesion state between the adhesive layer andthe optical film is fixed while the optical film and the adhesive layerare kept stuck together.

[0024] In one embodiment of the invention, the adhesive layer is made ofan ultraviolet-curable resin.

[0025] Preferably, the step of curing the adhesive layer includes thestep of leaving the adhesive layer and the optical film standing whilethe adhesive layer and the optical film are kept stuck together. Morepreferably, the step of curing the adhesive layer includes the step ofleaving the adhesive layer and the optical film standing while theadhesive layer and the optical film are kept stuck together so that thegel fraction of the adhesive layer is 50 wt % or more.

[0026] A surface protection film may be provided on the adhesive layerfor protecting the adhesive layer, the thickness t of the surfaceprotection film being in a range of 0.035 mm≦t≦0.2 mm, and the methodmay further includes the step of peeling off the surface protection filmbefore the step of pressing the optical film against the adhesive layer.

[0027] A rough surface may be bonded to the other of the opposingsurfaces of the transparent support via an adhesive layer. Preferably,the rough surface is a surface of a film produced by drawing. The roughsurface may include a region having a roughness Rt1 satisfying Rt1>2 μmwhen the roughness Rt1 is defined as the distance between the highestcrest and the deepest trough within a range of a length evaluated.

[0028] Preferably, the transparent support has a roughness Rt2satisfying Rt2≦2 μm when the roughness Rt2 is defined as the distancebetween the highest crest and the deepest trough within a range of alength evaluated.

[0029] The optical film may be a lens sheet having a plurality of lensesformed on at least one surface, and may be pressed against the adhesivelayer with the surface having the plurality of lenses facing theadhesive layer. Preferably, the lens sheet is a lenticular sheet havinga plurality of semi-cylindrical lenticules arranged in parallel with oneanother, and the lenticular sheet is pressed against the adhesive layerwith a force applied in the direction of the extension of the lenticuleswith the surface having the plurality of lenticules facing the adhesivelayer. Alternatively, the optical film may be a prism sheet having aplurality of prisms.

[0030] According to the second aspect of the present invention, alaminate film is provided. The laminate film includes: a transparentsupport having two opposing surfaces; an adhesive layer formed on one ofthe two opposing surfaces of the transparent support; and an opticalfilm bonded to the transparent support via the adhesive layer. In thefilm, the adhesive layer is made of a material of which the cured statechanges by application of external energy, and the transparent supporthas a roughness Rt satisfying Rt≦2 μm when the roughness Rt is definedas the distance between the highest crest and the deepest trough withina range of a length evaluated.

[0031] Preferably, the adhesive layer has a gel fraction of 50 wt % ormore.

[0032] The optical film may be a lens sheet having a plurality of lensesformed on at least one surface, and may be pressed against the adhesivelayer with the surface having the plurality of lenses facing theadhesive layer. The optical film may be a prism sheet having a pluralityof prisms.

[0033] According to the third aspect of the present invention, a methodfor fabricating a display device including a display element and anoptical film placed on the viewer's side of the display element. Themethod includes the steps of: producing the display element; and bondingthe optical film to the surface of the display element on the viewer'sside via an adhesive film; wherein the adhesive film includes atransparent support having a first adhesive layer formed on one of twoopposing surfaces, the first adhesive layer being made of a material ofwhich the cured state changes by application of external energy, and thestep of bonding the optical film to the surface of the display elementon the viewer's side includes the steps of: applying external energy tothe first adhesive layer; pressing the optical film against the firstadhesive layer to stick the optical film and the first adhesive layertogether; curing the first adhesive layer to a degree of hardness withwhich the adhesion state between the optical film and the first adhesivelayer is fixed while the optical film and the first adhesive layer arekept stuck together; and after curing of the first adhesive layer,bonding the other of the two opposing surfaces of the transparentsupport and the display element via a second adhesive layer.

[0034] In a preferred embodiment of the invention, the display elementis a liquid crystal display element including a pair of substrates, aliquid crystal material sandwiched between the pair of substrates, andoptical characteristic changing means for changing the opticalcharacteristics of incident light placed on at least the viewer's sideof the pair of substrates, and the optical film is bonded to the liquidcrystal display element by bonding the optical characteristic changingmeans and the transparent support of the adhesive film together via thesecond adhesive layer.

[0035] The first adhesive layer may be made of an ultraviolet-curableresin.

[0036] The step of curing the first adhesive layer may include the stepof leaving the first adhesive layer and the optical film standing whilethe first adhesive layer and the optical film are kept stuck together.

[0037] The step of curing the first adhesive layer may include the stepof leaving the first adhesive layer and the optical film standing whilethe first adhesive layer and the optical film are kept stuck together sothat the gel fraction of the first adhesive layer is 50 wt % or more.

[0038] Preferably, a surface protection film is provided at least on thefirst adhesive layer for protecting the first adhesive layer, thethickness t of the surface protection film being in a range of 0.035mm≦t≦0.2 mm, and the method may further include the step of peeling offthe surface protection film before the step of pressing the optical filmagainst the first adhesive layer.

[0039] Preferably, the surface of the display element to be bonded withthe second adhesive layer includes a region having a roughness Rt1satisfying Rt1>2 μm when the roughness Rt1 is defined as the distancebetween the highest crest and the deepest trough within a range of alength evaluated.

[0040] Preferably, the transparent member has a roughness Rt2 satisfyingRt2≦2 μm when the roughness Rt2 is defined as the distance between thehighest crest and the deepest trough within a range of a lengthevaluated.

[0041] The optical characteristic changing means may be a polarizingplate. Alternatively, the optical characteristic changing means may be aphase plate.

[0042] The optical film may be a lens sheet having a plurality oflenses, and may be pressed against the first adhesive layer with thesurface having the plurality of lenses facing the first adhesive layer.

[0043] Preferably, the lens sheet is a lenticular sheet having aplurality of semi-cylindrical lenticules arranged in parallel with oneanother, and the lenticular sheet is pressed against the first adhesivelayer with a force applied in the direction of the extension of thelenticules with the surface having the plurality of lenticules facingthe first adhesive layer. Alternatively, the optical film may be a prismsheet having a plurality of prisms.

[0044] According to the fourth aspect of the present invention, A methodfor fabricating a display device including a display element and a lenssheet placed on the viewer's side of the display element is provided.The lens sheet has a plurality of lenticules arranged in parallel withone another. The method includes the steps of: producing the displayelement; forming an adhesive layer on the viewer's side of the displayelement; placing the lens sheet so that the lens surfaces of thelenticules face the adhesive layer; and pressing the lens sheet againstthe adhesive layer by applying a force in the direction of the extensionof the lenticules.

[0045] Hereinafter, the function of the present invention will bedescribed.

[0046] In the method for fabricating a laminate film according to thepresent invention, after external energy is applied to an adhesive layermade of a material of which the cured state changes by application ofexternal energy, an optical film (e.g., lens sheet) is pressed againstthe adhesive layer. This process step is carried out while the materialis in B stage (intermediate cured state). The adhesive layer is thencured to a degree of hardness with which the adhesion state between theoptical film and the adhesive layer no more changes, to thereby completea laminate film. After this curing step, the material of the adhesivelayer is in C stage (completely cured state) or near C stages. In such alaminate film, the adhesion state of the optical film is fixed by atransparent support via the adhesive layer. Therefore, when the laminatefilm is bonded to a rough surface, the shape of the rough surface isprevented from being transferred to the optical film and influencing theoptical characteristics of the optical film. The effect of the presentinvention is especially great for an optical film having concave andconvex portions formed on the surface thereof in contact with theadhesive layer in which the area of the contact region between eachconvex portion and the adhesive layer influences the opticalcharacteristics of the optical film.

[0047] In particular, when the adhesive layer for bonding the opticalfilm and the transparent support together is made of a photocurableresin, the optical film and the transparent support can be easily bondedand fixed together. This reduces generation of defects due to scars andexternal force.

[0048] By placing a surface protection film on the outer surface of theadhesive layer of the adhesive film and setting the thickness t of thesurface protection film in the range of 0.035 mm≦t≦0.2 mm, the adhesivelayer is prevented from deforming due to existence of foreign mattersand external force before curing. As a result, bonding between the lightdiverging element and the transparent member is facilitated.

[0049] The method for fabricating a display device according to thepresent invention also has the function described above in relation withthe method for fabricating a laminate film. In particular, in the caseof using a liquid crystal display element as the display element, wavestend to be generated on the surface of a polarizing plate or a phaseplate of the display element. When an optical film is bonded to thepolarizing plate or the phase plate in an attempt to improve thecharacteristics of the display element, the waves of the polarizingplate or the phase plate are transferred to the optical film. Accordingto the fabrication method of the present invention, however, thelaminate film is bonded to the display element after the adhesive layeris cured to a degree that the adhesion state between the optical filmand the adhesive layer no more changes. Therefore, it is possible toprevent the uneven surface of the display element from influencing theoptical film, and thus prevent deterioration in display quality. Inparticular, when a lens sheet as the optical film is bonded to a liquidcrystal display element by the fabrication method according to thepresent invention, the resultant liquid crystal display device canexhibit high display quality with an improved viewing anglecharacteristic.

[0050] By placing a surface protection film on the outer surface of theadhesive layer formed on the transparent support and setting thethickness t of the surface protection film in the range of 0.035mm≦t≦0.2 mm, the adhesive layer is prevented from deforming due toexistence of foreign matters and external force before curing. As aresult, bonding between the optical film and the transparent support isfacilitated. In particular, spot defects and bar shaped defectsinfluence the optical performance of the light diverging element. Adefect having a diameter of 0.1 mm or more will be observed as a paneldefect, causing significant deterioration in display quality.

[0051] By controlling the thickness of the surface protection film, thenumber of spot defects and bar-shaped defects can be markedly reduced.For example, while the number of defects is 200 pieces/m² when thethickness of the surface protection film is 0.02 mm, it can be as smallas 50 pices/m² when the thickness is 0.035 mm. For a 20-inch liquidcrystal display device, for example, about 25 defects can be reduced to10 pieces or less. The display quality therefore improves.

[0052] Although a thicker surface protection film can reduce the numberof defects, it increases the cost since the material cost is higher.Therefore, the thickness is preferably 0.2 mm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053]FIG. 1 is a schematic illustration of a liquid crystal displaydevice in Embodiment 1 of the present invention.

[0054]FIGS. 2A and 2B are views of examples of arrangement of R, G, andB pixels.

[0055]FIGS. 3A and 3B are views illustrating a lens sheet in Embodiment1 of the present invention.

[0056]FIG. 4 is a view illustrating a surface illuminant in Embodiment 1of the present invention.

[0057]FIGS. 5A, 5B, 5C, and 5D are views illustrating a fabricationprocess for the liquid crystal display device in Embodiment 1 of thepresent invention.

[0058]FIGS. 6A, 6B, 6C and 6D are views illustrating the fabricationprocess for the liquid crystal display device in Embodiment 1 of thepresent invention.

[0059]FIGS. 7A and 7B are views illustrating the fabrication process forthe liquid crystal display device in Embodiment 1 of the presentinvention.

[0060]FIGS. 8A and 8B are views illustrating a modification of thefabrication process for the liquid crystal display device in Embodiment1 of the present invention.

[0061]FIG. 9 is a view illustrating the roller moving direction in theprocess of pressing the lens sheet against an adhesive layer.

[0062]FIG. 10 is a view illustrating the roller moving direction in theprocess of pressing the lens sheet against the adhesive layer.

[0063]FIG. 11 is a schematic illustration of the adhesion state betweenlens convex portions of the lens sheet and the adhesive layer.

[0064]FIG. 12 is a view showing the luminance characteristic of theliquid crystal display device in Embodiment 1 of the present invention.

[0065]FIG. 13 is a view showing the viewing angle characteristic of theliquid crystal display device in Embodiment 1 of the present invention.

[0066]FIG. 14 is a schematic illustration of a liquid crystal displaydevice in Embodiment 2 of the present invention.

[0067]FIG. 15 is a view illustrating the display principle of areflection type liquid crystal display device.

[0068]FIGS. 16A and 16B are views illustrating a prism sheet inEmbodiment 2 of the present invention.

[0069]FIGS. 17A, 17B, 17C, and 17D are views illustrating a fabricationprocess for the liquid crystal display device in Embodiment 2 of thepresent invention.

[0070]FIGS. 18A, 18B, 18C and 18D are views illustrating the fabricationprocess for the liquid crystal display device in Embodiment 2 of thepresent invention.

[0071]FIGS. 19A and 19B are views illustrating the fabrication processfor the liquid crystal display device in Embodiment 2 of the presentinvention.

[0072]FIGS. 20A and 20B are views illustrating a modification of thefabrication process for the liquid crystal display device of Embodiment2 of the present invention.

[0073]FIG. 21 is a view illustrating an offset of the optical axis inthe liquid crystal display device in Embodiment 2 of the presentinvention.

[0074]FIGS. 22A and 22B are views illustrating waves on a polarizingplate.

[0075]FIGS. 23A and 23B are views for explaining deterioration indisplay quality due to waves on a polarizing plate.

DETAILED DESCRIPTION OF THE INVENTION

[0076] The present inventors have found out for the first time that theprior art problem described above, that is, the problem that the displayquality greatly deteriorates when a light diverging element such as amicrolens array sheet is placed on the surface of a polarizing plate,occurs due to the fact that waves on the polarizing plate influence thecontact state between the concave and convex shaped surface of themicrolens array sheet and an adhesive layer. The present invention hasbeen achieved based on this finding.

[0077] Hereinafter, embodiments of the present invention will bedescribed with reference to the relevant drawings.

[0078] (Embodiment 1)

[0079]FIG. 1 is a cross-sectional view of a liquid crystal displaydevice used in Embodiment 1 of the present invention. Referring to FIG.1, the liquid crystal display device in this embodiment includes asurface illuminant 11, a liquid crystal display element 10 and alaminate film 17 which includes an adhesive film 16, and a lens sheet(lens film) 15 as an optical film.

[0080] The liquid crystal display element 10 is essentially including:an active matrix substrate 13 a including thin film transistors (TFTs),transparent pixel electrodes, and the like formed in a matrix on atransparent substrate made of glass or plastic; a counter substrate 13 bincluding transparent electrodes and color filters formed on atransparent substrate made of glass or plastic; liquid crystal material14 as a display medium sealed in a space between the two substrates; anda pair of polarizing plates (polarizing films) 12 a and 12 b placed tosandwich the two substrates.

[0081] In this embodiment, twisted nematic (TN) liquid crystal materialhaving a twist angle of 90 degrees was used as the liquid crystalmaterial 14. As the liquid crystal display element 10, various typesdifferent in the number of pixels and the size are available. In thisembodiment, used was a liquid crystal display element having a screensize of 20 inches in a diagonal line (304.8 mm×406.4 mm), a stripe arrayof R, G, and B pixels shown in FIG. 2A with the number of pixels of 640(each of R, G, B) horizontally×480 vertically, and a horizontal pixelpitch Ph of 0.212 mm and a vertical pixel pitch Pv of 0.635 mm.

[0082] The color filters are not necessarily provided on the countersubstrate 13 b. For example, it may be formed on the pixel electrodes ofthe active matrix substrate 13 a.

[0083] On the outer surface of the polarizing plate 12 b located on theviewer's side of the liquid crystal display element 10, the lens sheet15 is placed via the adhesive film 16 including an adhesive layer (firstadhesive layer) 16 a, a transparent support 16 b, and another adhesivelayer (second adhesive layer) 16 c.

[0084] In this embodiment, as the lens sheet 15, used was a lenticularsheet having a plurality of semi-cylindrical lenticules arranged inrows. Note that the lens sheet denoted by the reference numeral 30 inFIG. 3 is the same as the lens sheet 15 in FIG. 1. The lenticular sheet30 was positioned so that the lenticules extend in parallel with thehorizontal (lateral) direction of the screen of the liquid crystaldisplay element.

[0085] In this embodiment, the lenticular sheet 30 was produced in thefollowing manner. First, an ultraviolet-curable resin (Z9001, refractiveindex n=1.59) manufactured by JSR Co., Ltd. was dropped in a mold in ashape of repeated concave portions. The ultraviolet-curable resin wasthen irradiated with 1.0 J/cm² ultraviolet light, to thereby transferand form repeated convex portions on a base plate 33. As the base plate33, an ARTON film manufactured by Japan Synthetic Rubber Co., Ltd. wasused. In this way, a lenticular sheet having a pitch P1 of 0.05 mm and aheight h of 0.015 mm was produced.

[0086] A light-shading layer 32 was formed over the entire surface oflenticules 31 for prevention of surface reflection of the lenticularsheet 30. More specifically, the light-shading sheet 32 was formed inthe following manner. An organic material containing a black pigmentdispersed therein was applied to the lenticules 31 by printing. Theorganic material was then irradiated with 1.5 J/cm² ultraviolet lightand cured. The thickness of the light-shading layer 32 was controlled tobe about 0.005 mm so that the total light transmittance of thelenticular sheet 30 was 70%.

[0087] Although the luminance of the liquid crystal display deviceincreases as the total light transmittance is higher, reduction in theluminance of the liquid crystal display device is negligibly small aslong as the total light transmittance is 50% or more.

[0088]FIG. 4 illustrates the surface luminant used in this embodiment.In FIG. 4, the surface luminant 11 in FIG. 1 is denoted by the referencenumeral 40.

[0089] The surface luminant 40 used in this embodiment is of a sidelighting type, which is essentially constructed of cold-cathode tubes 41a and 41 b, reflectors 42 a and 42 b surrounding the cold-cathode tubes41 a and 41 b, a diffusion reflection sheet 47, a light conductor 43with silk printing 44 formed thereon, a diffusing sheet 45 placed on thelight out-going side, and a DBEF film 46 (manufactured by 3M Ltd.). Thesurface luminant 40 having the above construction can be produced by aknow method, and thus the description thereof is omitted here.

[0090] Next, the laminate film used in this embodiment will bedescribed.

[0091] The lens sheet 15 is bonded to the polarizing plate 12 b of theliquid crystal display element on the viewer's side as shown in FIG. 1.In this bonding, if an adhesive layer such as a two-sided adhesive tapeis first formed on the polarizing plate 12 b and then the lens sheet 15is bonded to the adhesive layer, unevenness of the surface of thepolarizing plate 12 b, in particular, waves on the surface aretransferred to the optical film, and the influence of the unevenness isreflected on the surface of the lens sheet 15, resulting in variation inoptical characteristics.

[0092] In particular, in this embodiment, the lens sheet is placed sothat the concave and convex portions face the adhesive layer and thelens tips are buried in the adhesive layer. Since a normal adhesivelayer has a refractive index similar to that of the lens sheet material,the lens tips buried in the adhesive layer no more function as a lenssatisfactorily. To state differently, the contact region between an airlayer existing between the lens sheet and the adhesive layer and thelens sheet serves to generate refraction required for lens effect.Therefore, the size and in-plane uniformity of the contact areas betweenthe lens tips and the adhesive layer greatly influence the lenscharacteristics.

[0093] In view of the above, if the contact area between the lens tipand the adhesive layer is relatively large in some portion of the lenssheet, while it is relatively small in the other portion of the lenssheet, the optical characteristics (lens characteristics) of the lenssheet are distorted in the screen plane.

[0094] If the concave and convex surface of the optical sheet isdirectly bonded to the uneven surface of the backing layer such as thepolarizing plate via the adhesive layer as described above, the surfaceunevenness (waves) of the polarizing plate causes variation in thecontact areas between the lens tips of the lens sheet and the adhesivelayer in the sheet plane. As a result, the lens characteristics of thelens sheet are distorted reflecting the unevenness and waves of thebacking layer.

[0095] To prevent the above problem, in this embodiment, the transparentsupport 16 b having a predetermined flatness and the lens sheet 15 arepressed against each other via the adhesive layer 16 a. The adhesivelayer 16 a is then cured to a predetermined hardness, that is, to adegree of hardness with which the adhesion state between the opticalfilm and the adhesive layer no more changes. Thereafter, the resultantlaminate film of the lens sheet 15 and the transparent support 16 bondedtogether is bonded to the polarizing plate via the adhesive layer 16 c.Thus, the contact state between the lens sheet 15 and the adhesive layer16 a can be kept constant by the transparent support 16 b having apredetermined flatness. Therefore, when the laminate film including thelens sheet 15 is bonded to the polarizing plate in the subsequentprocess, the contact state between the lens sheet 15 and the adhesivelayer 16 a is prevented from being influenced by the unevenness such aswaves on the surface of the polarizing plate, and thus thecharacteristics of the optical film are not distorted.

[0096] The flatness of the transparent support will be described.

[0097] Table 1 below shows the results of examination by the presentinventors on the influence of the surface flatness (roughness) of thebacking film on the optical film when the optical film is bonded to thebacking film. TABLE 1 Roughness of backing Rt Influence of backing Rt >2 μm X not acceptable 2 μm ≧ Rt ≧ 1.5 μm Δ acceptable 1.51 μm > Rt > 1μm ◯ good 1 μm ≧ Rt ⊚ excellent

[0098] The flatness (roughness) Rt is defined as the distance betweenthe highest crest and the deepest trough within the range of a lengthevaluated. As is found from Table 1, when the roughness Rt of thebacking film is 2 μm or less, the influence of the surface shape of thebacking film on the optical characteristics of the optical film isacceptable. In the fabrication method of the present invention,therefore, the transparent support is made of a material having aroughness Rt of 2 μm or less. As is also found from Table 1, theroughness Rt is preferably less than 1.5 μm, more preferably equal to orless than 1 μm.

[0099] On the contrary, a film produced by drawing a material in onedirection, such as a polarizing plate and a phase plate, may have aregion having a roughness Rt exceeding 2 μm due to generation of waveson the surface and the like. A plastic substrate, also, may have aregion having a roughness Rt exceeding 2 μm. Moreover, even when theroughness Rt of the surface to which the optical film is to be bonded(surface of a polarizing plate and a phase plate) is less than 2 μm, anadhesive layer formed for adhesion of the optical film may have a scaror deformation due to external force exceeding 2 μm. For these reasons,the method for fabricating a laminate film of the present invention isespecially effective for the case of bonding the optical film to asurface that may include a region having a roughness Rt exceeding 2 μm.

[0100] Hereinafter, referring to FIGS. 5A to 5D, 6A to 6D, 7A and 7B,and 8A and 8B, a method for fabricating a laminate film and a method forfabricating a display device according to the present invention will bedescribed.

[0101]FIG. 5A shows a cross-section of an adhesive film 50 in the stateprior to the bonding with the optical film. The adhesive film 50includes a transparent support 53 for supporting the optical film in theflat state, and adhesive layers 52 and 54 formed on both surfaces of thetransparent support 53. Transparent separators (surface protection film)51 a and 51 b are formed on the outer surfaces of the adhesive layers 52and 54 for protecting these layers. At least the adhesive layer 52, outof the adhesive layers 52 and 54, to which the optical film is to bebonded, is made of a material of which the cured state changes byapplication of external energy, such as a photocurable resin. Note thatthe adhesive layers 52, 54, the transparent support 53 in FIG. 5Acorrespond to the adhesive layers 16 a, 16 c and the transparent support16 b in FIG. 1.

[0102] In this embodiment, a PET film having a thickness of 0.075 mm wasused as the transparent support 53. The thickness of the transparentsupport 53 is preferably in the range of about 25 μm to about 200 μm inview of an ease of handling. A photocurable resin was used for theadhesive layer 52. A postcurable UV (ultraviolet) resin is preferablyused as the photocurable resin for the adhesive layer 52. Thepostcurable UV resin is, for example, disclosed in Japanese Laid-OpenPatent No. 9-279103 (Sekisui Chemical Co., Ltd.), the contents of whichare hereby incorporated by reference. The curing reaction (e.g.,cationic polymerization) of the postcurable UV resin is initiated by anirradiation of ultraviolet light, and the reaction proceeds slowly atthe room temperature. Accordingly, while the curing reaction proceeds,that is, before the resin is completely cured, an object (e.g., lenssheet) can be adhered to the adhesive layer 52 without being fixed. Anacrylic resin was used for the adhesive layer 54. As the transparent 51a and 51 b, a PET film having a thickness of 0.05 mm was used.

[0103] The transparent separators 51 a and 51 b are formed to preventdefects from occurring due to existence of foreign matters generated inthe processes of bonding to the lens sheet and bonding to the polarizingplate to be described later, and are peeled off immediately before thesebonding processes. The thickness of the separators 51 a and 51 b is notlimited to that described above, but is determined so as to minimize thenumber of defects due to scars.

[0104] Table 2 below shows the thickness of the separators and thedensity of defects having a diameter of 0.1 mm or more. TABLE 2Thickness of Density of Number of separator defects defects Evaluationof (mm) (pcs./m²) (pcs.) appearance 0.02 200 25 X not acceptable 0.03125 15 X not acceptable 0.035 50 6 Δ acceptable 0.045 20 3 ◯ good 0.0510 1 ⊚ excellent 0.20 2 0 ⊚ excellent

[0105] As shown in Table 2, the density of defects due to scars changesby changing the thickness of the separators, and the number of defectschanges with the screen size. In the case of a liquid crystal displayelement having a screen size of 20 inches in a diagonal line, the numberof defects is as large as 25 pieces when the thickness of the separatorsis 0.020 mm. The display quality is deteriorated with such a largenumber of defects. When the thickness of the separators is increased to0.035 mm or more, the number of defects can be reduced to 10 pieces orless, which falls within the range in which no influence is recognizedin appearance.

[0106] The adhesive film 50 having the above construction is bonded tothe lens sheet in the following manner.

[0107] First, the separator 51 a covering the adhesive layer 52 made ofa photocurable resin is peeled off (FIG. 5B), and the adhesive layer 52is irradiated with light 5 a (FIG. 5C). The reason why the adhesivelayer 52 is irradiated with light after the separator is peeled off isto enhance the light sensitivity of the adhesive layer. Alternatively,the irradiation with ultraviolet light may be performed before theseparator is peeled off. In this case, however, the irradiation must beperformed in consideration of absorption of ultraviolet light by theseparator (about 20%). In this embodiment, a metal halide lamp was usedto irradiate the adhesive layer with the ultraviolet light 5 a. Theamount of irradiation was 1.6 J/cm².

[0108] Next, the lens sheet 55 is pressed against the adhesive layer 52.In this step, the material of the adhesive layer 52 is in B stage(intermediate cured state). In this embodiment, as shown in FIG. 5D, aroll-to-roll method using rollers 5 b and 5 c was employed to press thelens sheet 55 against the adhesive layer 52. The adhesive layer 52 isthen cured to a degree of hardness with which the lens sheet 55 is fixedto the transparent support 53 via the adhesive layer 52. After thiscuring step, the material of the adhesive layer 52 is in C stage(completely cured state) or near C stage. In this embodiment, theadhesive layer 52 was cured by leaving the adhesive layer 52 standing atroom temperature for 24 hours together with the lens sheet 55 keptpressed against the adhesive layer 52. In this way, a laminate includingthe adhesive film and the lens sheet is obtained (FIG. 6A).

[0109] The process of curing the adhesive layer 52 will be described.

[0110] The gel fraction of the adhesive layer 52 changes depending onthe material, the curing conditions, and the like. Depending on the gelfraction, the degree of deterioration in display quality due to thetransfer of waves on the polarizing plate to the lens sheet changes.Table 3 below shows the relationship between the gel fraction and waveson the polarizing plate. TABLE 3 Gel fraction (wt %) Wave on polarizingplate 30 X not acceptable 40 X not acceptable 50 Δ acceptable 60 ◯ good70 ◯ good 80 ⊚ excellent 90 ⊚ excellent 95 ⊚ excellent

[0111] From Table 3, it is found that when the gel fraction is 50 wt %or more, the influence of waves on the surface of the polarizing platecan be suppressed and thus acceptable display quality is obtained. Inthis embodiment, the adhesive layer 52 was cured until the gel fractionof 75 wt % was obtained by leaving the adhesive layer 52 standing atroom temperature for 24 hours.

[0112] The gel fraction was measured in the following manner. First, theweight w1 of a portion of the adhesive layer as a sample left for 24hours after light irradiation was measured (w1=0.1 g in this example),and the sample was immersed in ethyl acetate (50 cc) for 12 hours. Theethyl acetate with the sample was then filtered, dried (at 110° C. for30 minutes), and then left standing at room temperature for 30 minutes.The weight w2 of the resultant gelled sample was measured, and w2/w1×100wt % was calculated to obtain the gel fraction.

[0113] The other separator 51 b is then peeled off (FIG. 6B), a laminatefilm 56 is provided, and the laminate film 56 is bonded to a polarizingplate 57 a. In this embodiment, as shown in FIG. 6C, the adhesive layer54 and the polarizing plate 57 a were pressed against with each otherusing the rollers 5 b and 5 c.

[0114] Finally, the polarizing plate 57 a bonded with the laminate film56 (see FIG. 6D) is bonded to the liquid crystal display element. Inthis embodiment, as shown in FIG. 7A, the polarizing plate 57 a waspressed against a substrate 58 a of the liquid crystal display elementon the viewer's side using the rollers 5 b and 5 c. In this way, asshown in FIG. 7B, there is attained a liquid crystal display devicehaving a construction where the polarizing plates 57 a and 57 b areplaced on the outer surfaces of the pair of substrates 58 a and 58 bsandwiching a liquid crystal material 59 as a display medium, and thelens sheet 55 is placed on the outer surface of the polarizing plate 57a located on the viewer's side of the liquid crystal display element viathe adhesive film.

[0115] The process of bonding the lens sheet to the polarizing plate andthe liquid crystal display element is not limited to that describedabove. Any other process may be adopted as long as the lens sheet can befixed to the adhesive film 50 before the lens sheet 55 is bonded to thepolarizing plate 57 a by pressing the lens sheet 55 against the adhesivefilm 50 and curing the adhesive layer 52 in the adhesive film 50 sosufficiently that no change is allowed in the adhesion state between thelens sheet 55 and the adhesive layer 52. By fixing the lens sheet 55 asdescribed above, it is possible to reduce the occurrence that the unevensurface of the polarizing plate 57 a, in particular, waves on thesurface thereof change the in-plane distribution of the opticalcharacteristics of the optical film and thus adversely influence thedisplay quality when the lens sheet 55 is bonded to the polarizing plate57 a via the adhesive film 50 in a subsequent process. Therefore, thebonding process may proceed as shown in FIGS. 8A and 8B, for example,where the polarizing plate 57 a is previously bonded to the substrate 58a of the liquid crystal display element on the viewer's side, and thenthe laminate film 56 including the lens sheet 55 and the adhesive filmsand so on is pressed against the polarizing plate 57 a.

[0116] The adhesive layer 54 may be formed on the surface of thepolarizing plate 57 a, not on the transparent support 53 of the adhesivefilm 50. In this case, also, the lens sheet 55 and the adhesive film 50are bonded to each other, and after the adhesive layer 52 is curedsufficiently so that the lens sheet 55 can be fixed to the adhesivelayer 52 in a desired adhesion state, the resultant laminate of the lenssheet 55 and the adhesive film 50 is bonded to the polarizing plate 57a. By this process, also, it is possible to reduce the occurrence thatthe uneven surface of the polarizing plate 57 a, in particular, waves onthe surface thereof adversely influence the surface of the lens sheet55.

[0117] As described above, by pressing the lens sheet 55 against theadhesive layer 52 of the adhesive film 50 and then curing the adhesivelayer 52 sufficiently, the concave and convex shape of the lens arrayformed on the lens sheet 55 can be fixed to the transparent support 53,and thus the lens surface is prevented from deformation by externalforce. In addition, by curing the adhesive layer 52 sufficiently, theadhesion state of the lens sheet 55 is reliably fixed by the transparentsupport 53. By this fixation, when the polarizing plate 57 a is bondedto the surface of the transparent support 53 of the adhesive film 50 onthe side opposite to the lens sheet 55, the lens surface is preventedfrom being influenced by waves on the polarizing plate 57 a, and thusthe display quality can be improved.

[0118] In FIG. 5D, the direction of the movement of the rollers 5 b and5 c (bonding direction) is vertical to the direction of the extension ofthe lenticules. The roller movement direction is not limited to this,but may be in parallel with the direction of the extension of thelenticules. An example of the latter case is shown in FIGS. 9 and 10.FIG. 9 shows a cross-sectional view of the lens sheet 55, the adhesivelayer 52, and transparent support 53, and FIG. 10 shows a plan view ofthe adhesive layer 52, both of which illustrate the roller movingdirection in the process of pressing the lens sheet 55 against theadhesive layer 52. As shown in FIGS. 9 and 10, a pressure is applied onthe lens sheet 55 with the roller 5 b in the direction in parallel withthe extension of the lenticules. By this pressing, uniform pressure isapplied outward from the center of the convex portion of each lenticule(in the direction vertical to the extension of the lenticules). As aresult, as shown in FIG. 11, each adhesion region of the lens of thelens sheet 55 to the adhesive layer 52 can be a region symmetrical withrespect to the center of the lens convex portion and thus the viewingangle characteristic can be expanded symmetrically. It should be notedthat in the steps shown in FIGS. 7A and 8A, since the contact statebetween the lens sheet 55 and the adhesive layer 52 has already beenfixed, the shape of the lens convex portions does not change inparticular in whichever direction the pressure is applied with theroller.

[0119] The luminance characteristic and the viewing angle characteristicof the liquid crystal display device in this embodiment fabricated asdescribed above were compared with a conventional liquid crystal displaydevice having no lens sheet. The results are shown in FIGS. 12 and 13.

[0120]FIG. 12 shows the luminance characteristic of the liquid crystaldisplay device in the vertical direction with respect to the screen (thedirection in which the plurality of lenticules are arranged, that is,the direction vertical to the extension of the lenticules). FIG. 13shows the viewing angle characteristic (relationship between the angleat which the screen is viewed and the contrast) of the liquid crystaldisplay device in the vertical direction with respect to the screen. InFIGS. 12 and 13, the bold line represents the characteristics of theliquid crystal display device in this embodiment, and the fine linerepresents the characteristics of a conventional TN liquid crystaldisplay device having no lens sheet. Both the luminance characteristicand the viewing angle characteristic were obtained by applying a voltagesignal to the liquid crystal display device to effect monochrome displayand measuring the luminance at positions in the vertical direction withrespect to the screen using a viewing angle measuring apparatus. Notethat the measurement of the luminance characteristic shown in FIG. 12was obtained by normalization with the luminance which is observed alonga normal to the screen of each liquid crystal display device.

[0121] As shown in FIG. 12, in the liquid crystal display device of thisembodiment, the rate of change of the luminance with the viewing angleis small, and also the change of the luminance with the viewing angle issmall, compared with the conventional liquid crystal display device. Asshown in FIG. 13, in the liquid crystal display device of thisembodiment, the front contrast is somewhat small compared with theconventional liquid crystal display device. However, the value of thecontrast ratio with respect to the viewing angle is higher than theconventional value, and reversal of an image is prevented. Therefore,the liquid crystal display device can provide a wide viewing anglecharacteristic.

[0122] Thus, in this embodiment, the photocurable adhesive layer formedon the transparent support is irradiated with light, and then the lenssheet is pressed against the adhesive layer. The adhesive layer is thenleft standing in this state until the adhesive layer is cured to adegree of hardness with which the adhesion state between the lens sheetand the adhesive layer is fixed. Thereafter, the lens sheet fixed to thetransparent support via the sufficiently cured adhesive layer is bondedto the polarizing plate via an adhesive layer. This suppresses theuneven surface of the polarizing plate, in particular, waves on thesurface thereof from adversely influencing the surface state of theoptical film. In addition, the optical film can be fixed and bondedwithout being peeled off.

[0123] A separator having a predetermined thickness is provided on theadhesive layer to which the optical film or the polarizing plate is tobe bonded. The separator is peeled off immediately before the bonding ofthe optical film or the polarizing plate to the adhesive layer. Thisreduces occurrence of scars and deformation due to external force, andthus a liquid crystal display device with reduced display defects can beprovided.

[0124] In this embodiment, a lenticular sheet was used as the lenssheet. The lens shape is not limited to this, but may preferably bechanged based on the direction in which the viewing angle is desired tobe wide. For example, when the viewing angle is desired to be wide inall directions, a sheet having a number of semispherical microlenses canbe used. When the viewing angle is desired to be wide in the right andleft directions, a sheet having lens arrays arranged in parallel withthe vertical direction of the screen can be used.

[0125] The material of the transparent support is not limited to PET,but a transparent resin material such as polycarbonate (PC), polymethylmethacrylate (PMMA), and triacetyl cellulose (TAC) may be used.

[0126] (Embodiment 2)

[0127] Embodiment 2 of the present invention will be described withreference to FIGS. 14 to 21.

[0128]FIG. 14 is a cross-sectional view illustrating a liquid crystaldisplay device used in Embodiment 2 of the present invention. Referringto FIG. 14, the illustrated liquid crystal display device, which is of areflection type, includes a reflection type liquid crystal displayelement 140 and a laminate film 147. The laminate film 147 includes atransparent member 145 and a prism sheet 146 as an optical film, and thetransparent member 145 includes a first adhesive layer 145 a, atransparent support 145 b, and a second adhesive layer 145 c.

[0129] The reflection type liquid crystal display element 140 isessentially including: an active matrix substrate 141 a including thinfilm transistors (TFTs) and transparent pixel electrodes arranged in amatrix and a reflector 142 formed on a substrate made of glass, plastic,a monocrystalline silicon, or the like; TN liquid crystal material 143having a twist angle of 45 degree; and a counter substrate 141 bincluding transparent electrodes and color filters. The substrates 141 aand 141 b are bonded together with a sealing agent with the liquidcrystal material 143 sealed therebetween. A λ/4 plate 144 b and apolarizing plate 144 a are placed on the outer surface of the countersubstrate 141 a of the reflection type liquid crystal display element140, that is, on the viewer's side.

[0130] Referring to FIG. 15, the display principle of the reflectiontype liquid crystal display element in this embodiment will bedescribed.

[0131] Incident illumination light 155 passes through a polarizing plate154 a and a λ/4 plate 154 b and is reflected by a reflector 152. Duringthis passing, the polarizing state of the illumination light 155 ismodulated in a liquid crystal layer 153, whereby the amount of lightout-going from the reflection type liquid crystal display element iscontrolled and thus an image is displayed.

[0132] More specifically, the polarizing plate 154 a is placed so thatthe transmission axis or the absorption axis thereof is at an angle of45° with respect to the phase retardation axis (slow axis) or the phaseadvance axis (fast axis) of the λ/4 plate 154 b. Linearly polarizedlight out of the illumination light 155 that has passed through thepolarizing plate 154 a is changed to a circularly polarized light by theλ/4 plate 154 b before it is incident on the reflection type liquidcrystal display element. In the case where the liquid crystal layer 153of the liquid crystal display element does not modulate the incidentcircularly polarized light, the direction of rotation of the circularlypolarized light is reversed when it is reflected by the reflector 152.The reflected circularly polarized light returns through the λ/4 plate154 b to the polarizing plate 154 a, where the circularly polarizedlight is changed to linearly polarized light orthogonal to thetransmission axis of the polarizing plate 154 a and thus absorbed. As aresult, black is displayed.

[0133] In the case where the liquid crystal layer 153 of the liquidcrystal display element modulates the incident circularly polarizedlight so that the circularly polarized light is reflected withoutchange, the reflected circularly polarized light returns through the λ/4plate 154 b to the polarizing plate 154 a, where the circularlypolarized light is changed to linearly polarized light matching with thetransmission axis of the polarizing plate 154 a and thus outputted. As aresult, color is displayed.

[0134] The directions of the transmission axis of the polarizing plate154 a and the phase retardation axis of the λ/4 plate 154 b aredetermined in consideration of the kind and the orientation direction ofthe liquid crystal material, the viewing angle characteristic, and thelike. As the phase plate, a layered structure of a λ/2 plate and a λ/4plate may be used.

[0135] In this embodiment, for color display, color filters of the threeprimary colors, red (R), green (G), and blue (B), are placed on thecounter substrate 141 b for respective pixels as described above. Coloris imparted to light passing through each of the color filters. The R,G, and B pixels can be arranged in various array patterns, such as thestripe array shown in FIG. 2A and a delta array shown in FIG. 2B, wherepicture elements are arranged repeatedly in the horizontal and verticaldirections.

[0136] The number of pixels and the size of each pixel vary with thepanel size. In this embodiment, used was a 3.9-inch reflection typeliquid crystal display element in the stripe array with the number ofpixels of 320 (each of R, G, and B) horizontally×240 vertically, and ahorizontal pixel pitch Ph of 0.0826 mm and a vertical pixel pitch Pv of0.248 mm.

[0137] The color filters are not necessarily provided on the countersubstrate. For example, it may be formed on the pixel electrodes of theactive matrix substrate.

[0138] The prism sheet 146, which is bonded to the outer surface of thepolarizing plate 144 a on the viewer's side via the transparent member145, will be described with reference to FIG. 16. Note that the prismsheet denoted by the reference numeral 166 in FIG. 16 is the same as theprism sheet shown in FIG. 14.

[0139] The prism sheet 166 includes a plurality of prisms 166 a arrangedin parallel with one another. In this embodiment, the plurality ofprisms are arranged to extend in a direction parallel to the lateraldirection of the screen of the liquid crystal display element, for thepurpose of widening the viewing angle in the upward and downwarddirections with respect to the screen.

[0140] The prism sheet 166 is formed using a mold in a shape of repeatedprisms, for example, by transferring the repeated prism shape to acrylicmaterial by injection molding. In this embodiment, formed were theprisms 166 a having a pitch P2 of 0.10 mm, a height h2 of 0.027 mm, anangle θ1 of 15°±2°, and an angle θ2 of 90°±2°.

[0141] A reflection prevention film (not shown) may be formed on thesurface of the prism sheet 166 opposite to the prism-formed surface.This improves the transmittance of the prism sheet 166. In thisembodiment, a reflection prevention film including a MgF₂ thin film anda SiO₂ thin film each having a thickness of about 0.1 μm layeredalternately was directly formed by evaporation. Reflection energy can bereduced by interference between the thin films. With this reflectionprevention film, the surface reflection of about 4% was successfullyreduced to 1% or less, and thus the transmittance of the prism sheet 166improved.

[0142] Next, the transparent member used in this embodiment will bedescribed in detail, followed by brief description of the method forfabricating a liquid crystal display device in this embodiment.

[0143] The transparent member 145 in FIG.14, including a transparentsupport 145 b and adhesive layers 145 a and 145 c formed on bothsurfaces of the transparent support 145 b, is produced using an adhesivefilm 170 shown in FIG. 17A. Note that the transparent support 145 b andthe adhesive layers 145 a and 145 c in FIG. 14 correspond to thetransparent support 173 and the adhesive layers 172 and 174 in FIG. 17A,respectively. As shown in FIG. 17A, adhesive layers 172 and 174 areformed on the opposing surfaces of a transparent support 173, and areprotected by separators 171 a and 171 b formed thereon.

[0144] At least one of the two adhesive layers to which the optical film(in this embodiment, the prism sheet) is to be bonded is made of amaterial of which the cured state changes by application of externalenergy, such as a photocurable resin. In this embodiment, the adhesivelayer 172 was formed of a photocurable resin, and the adhesive layer 174was formed of an acrylic resin. A PET film having a thickness of 0.075mm was used as the transparent support 173. As the separators 171 a and171 b, a PET film having a thickness of 0.05 mm was used. The thicknessof the separators is not limited to this, but is determined so as tominimize the number of defects due to scars, for example, as in thethickness of the separators used in Embodiment 1.

[0145] First, as in Embodiment 1, the prism sheet as the optical sheetis bonded to the adhesive film 170. Specifically, as shown in FIG. 17B,the separator 171 a covering the adhesive layer 172 of the adhesive film170 is peeled off, and as shown in FIG. 17C, the adhesive layer 172 isirradiated with light 17 a. Subsequently, as shown in FIG. 17D, theprism sheet 176 is pressed against the adhesive layer 172. In thisembodiment, a metal halide lamp was used to irradiate the adhesive layer172 with 1.6 J/cm² ultraviolet light, and then the prism sheet 176 waspressed against the adhesive layer 172 with rollers 17 b and 17 c.

[0146] With the prism sheet 176 kept pressed against the adhesive layer172, the adhesive layer 172 is cured to a degree that the adhesion statebetween the prism sheet 176 and the adhesive layer 172 is kept unchangedin the subsequent processes (FIG. 18A). Specifically, as described inEmbodiment 1, the adhesive layer 172 is desirably cured until a gelfraction of 50 wt % or more is obtained. In this embodiment, as inEmbodiment 1, the adhesive layer 172 was left standing at roomtemperature for 24 hours to obtain a gel fraction of about 75 wt %.

[0147] By curing the adhesive layer 172 as described above, thetransparent support 173 can support the prism sheet 176 in substantiallythe flat state. As a result, when the prism sheet 176 is bonded to arough surface having a somewhat uneven shape, such as the surface of thepolarizing plate, via the transparent support 173 in a subsequentprocess, transfer of the uneven shape of the rough surface to the prismsheet 176 can be reduced.

[0148] After curing of the adhesive layer 172, the separator 171 b ispeeled off (FIG. 18B), and a polarizing plate 175 is pressed against theadhesive layer 174 with the rollers 17 b and 17 c (FIG. 18C), to producea laminate including the prism sheet 176 and the polarizing plate 175bonded together via the adhesive film (FIG. 18D). The resultant laminateis bonded to the substrate of the reflection type liquid crystal displayelement on the viewer's side (FIG. 19A), to obtain the reflection typeliquid crystal display device in this embodiment (FIG. 19B).

[0149] The process of bonding the prism sheet 176 to the polarizingplate 175 and to the reflection type liquid crystal display element isnot limited to that described above. Any other method may be adopted aslong as the prism sheet can be fixed to the adhesive film before theprism sheet is bonded to the polarizing plate by pressing the prismsheet against the adhesive film and curing the adhesive layer existingbetween the prism sheet and the adhesive film so sufficiently that nochange is allowed in the adhesion state between the prism sheet and theadhesive layer in the subsequent processes. By fixing the prism sheet asdescribed above, it is possible to reduce the occurrence that the unevensurface of the polarizing plate, in particular, waves on the surfacethereof are transferred to the prism sheet and thus adversely influencethe display quality. Therefore, the bonding process may proceed as shownin FIGS. 20A and 20B, for example, where the polarizing plate 175 ispreviously bonded to a substrate 177 a of the liquid crystal displayelement on the viewer's side, and then the laminate of the prism sheet176 and the adhesive film is pressed against the polarizing plate 175.

[0150] The adhesive layer 174 may be formed on the surface of thepolarizing plate 175, not on the transparent support 173. In this case,also, the prism sheet 176 and the adhesive film 170 are bonded together,and after the adhesive layer 172 is cured sufficiently so that the prismsheet 176 can be fixed to the adhesive film 170 in a desired adhesionstate, the resultant laminate of the prism sheet 176 and the adhesivefilm 170 is bonded to the polarizing plate 175. By this process, also,it is possible to reduce the occurrence that the uneven surface of thepolarizing plate 175, in particular, waves on the surface thereofinfluence the surface of the prism sheet 176.

[0151] As described above, by pressing the prism sheet 176 against theadhesive layer 172 of the adhesive film 170 and then curing the adhesivelayer 172 sufficiently, the concave and convex shape of the prism arrayformed on the prism sheet 176 can be fixed to the transparent support173. The prism surface is therefore prevented from deformation byexternal force. In addition, by curing the adhesive layer 172sufficiently, the adhesion state of the prism sheet 176 is reliablyfixed by the transparent support 173. By this fixation, when thepolarizing plate 175 is bonded to the surface of the transparent support173 of the adhesive film on the side opposite to the prism sheet 176,the prism surface is prevented from being influenced by waves on thepolarizing plate 175, and thus the display quality can be improved.

[0152] In the reflection type liquid crystal display device in thisembodiment fabricated in the manner described above, as shown in FIG.21, illumination light incident on the display screen at an angle ofabout 30° from the normal to the display screen is reflected from thereflector to be output in the direction normal to the display screen.This allows a regular reflection image from the reflector to be observedas a display image, enabling bright display. In addition, regularreflection light from the surface of the prism sheet is reflected in adirection different from the direction in which the display image isreflected. Thus, the regular reflection light does not adverselyinfluence the display.

[0153] As described above, in the liquid crystal display device in thisembodiment, the laminate film including the prism sheet having aplurality of concave and convex portions and the adhesive film is bondedto the polarizing plate placed on the viewer's side of the liquidcrystal display element. In particular, the prism sheet is pressedagainst and fixed to the photocurable adhesive layer, and the opticalfilm is bonded to the polarizing plate via the transparent support. Withthis construction, waves generated on the surface of the polarizingplate can be absorbed and reduced. In addition, the prism sheet can befixed and bonded without being peeled off. The resultant liquid crystaldisplay device is free from deterioration in display quality.

[0154] The separator having a predetermined thickness is placed on theouter surface of the adhesive film to prevent generation of scars anddeformation due to external force during the bonding of the prism sheetto the adhesive layer. In this way, a liquid crystal display device withreduced display defects is provided.

[0155] The prism sheet is pressed against and fixed to the curableadhesive layer, and then the adhesive film is pressed against thepolarizing film. In this way, the optical film and the polarizing filmcan be bonded and fixed to each other. Thus, a fabrication methodcapable of preventing influence of waves on the surface of thepolarizing plate can be provided.

[0156] Note that the shape of the prism sheet used in this embodiment isnot limited to that described above, but can be appropriately selecteddepending on the refractive index of the prism sheet and the desiredillumination environment (direction of illumination light).

[0157] Thus, as described above, in the method for fabricating alaminate film according to the present invention, after external energyis applied to the adhesive layer made of a material of which the curedstate changes by application of external energy, the optical film ispressed against the adhesive layer. The adhesive layer is then cured toa degree of hardness with which the adhesion state between the opticalfilm and the adhesive layer is fixed. By the above method, it ispossible to obtain a laminate film including the optical film sustainedin substantially the flat state by the transparent support via theadhesive layer. When this laminate film is bonded to a polarizing plateor the like having waves generated on the surface thereof, it ispossible to prevent generation of in-plane variation in the surfacestate of the optical film due to the waves or the like, and thus uniformoptical characteristics is obtained for the optical film. Therefore, bycombining the laminate film with a display element, it is possible toovercome the problem of the display quality being deteriorated bydistortion of the lens characteristics.

[0158] In particular, by using a photocurable resin as the material ofwhich the cured state changes by application of external energy, theoptical film and the transparent support can be easily bonded and fixedtogether. It is therefore possible to reduce generation of defects dueto scars and external force.

[0159] By using a lens sheet having a plurality of microlens arrays asthe optical film, provided is a high-performance laminate film that canreduce distortion of the lens characteristics of the lens sheet that issensitive to the contact state with the adhesive layer, and can suppressdeterioration in display quality due to waves on the polarizing plateand due to generation of scars and deformation by external force.

[0160] By placing a surface protection film having a thickness t in therange of 0.035 mm≦t≦0.2 mm on the outer surface of the adhesive layer ofthe adhesive film, it is possible to prevent deformation of thepre-cured adhesive layer due to existence of foreign matters andexternal force and thus reduce the number of defects that maydeteriorate the display quality. As a result, bonding between theoptical film and the transparent member is facilitated.

[0161] In the method for fabricating a display device according to thepresent invention, the laminate film including the optical filmdescribed above is placed on the viewer's side of a display element.With this construction, it is possible to prevent the unevenness of thesurface, in particular, waves on the surface of the display element towhich the laminate film is bonded from being transferred to the opticalfilm, causing variation in optical characteristics. As a result, it ispossible to provide a display device in which the opticalcharacteristics including in particular the viewing angle characteristicare improved without deteriorating the display quality.

[0162] While the present invention has been described in a preferredembodiment, it will be apparent to those skilled in the art that thedisclosed invention may be modified in numerous ways and may assume manyembodiments other than that specifically set out and described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention which fall within the true spirit andscope of the invention.

What is claimed is:
 1. A method for fabricating a laminate film, thelaminate film comprising a transparent support having two opposingsurfaces and an optical film, the optical film being formed on one ofthe two opposing surfaces of the transparent support via a firstadhesive layer made of a material of which the cured state changes byapplication of external energy, the method comprising the steps of:applying external energy to the first adhesive layer; pressing theoptical film against the adhesive layer to stick the optical film andthe adhesive layer together; and curing the adhesive layer to a degreeof hardness with which the adhesion state between the adhesive layer andthe optical film is fixed while the optical film and the adhesive layerare kept stuck together.
 2. The method of claim 1, wherein the adhesivelayer is made of an ultraviolet-curable resin.
 3. The method of claim 1,wherein the step of curing the adhesive layer comprises the step ofleaving the adhesive layer and the optical film standing while theadhesive layer and the optical film are kept stuck together.
 4. Themethod of claim 1, wherein the step of curing the adhesive layercomprises the step of leaving the adhesive layer and the optical filmstanding while the adhesive layer and the optical film are kept stucktogether so that the gel fraction of the adhesive layer is 50 wt % ormore.
 5. The method of claim 1, wherein a surface protection film isprovided on the adhesive layer for protecting the adhesive layer, athickness t of the surface protection film being in a range of 0.035mm≦t≦0.2 mm, and the method further comprises the step of peeling offthe surface protection film before the step of pressing the optical filmagainst the adhesive layer.
 6. The method of claim 1, wherein a roughsurface is bonded to the other of the opposing surfaces of thetransparent support via a second adhesive layer.
 7. The method of claim6, wherein the rough surface is a surface of a film produced by drawing.8. The method of claim 6, wherein the rough surface includes a regionhaving a roughness Rt1 satisfying Rt1>2 μmwhen the roughness Rt1 isdefined as the distance between the highest crest and the deepest troughwithin a range of a length evaluated.
 9. The method of claim 1, whereinthe transparent support has a roughness Rt2 satisfying Rt2≦2 μmwhen theroughness Rt2 is defined as the distance between the highest crest andthe deepest trough within a range of a length evaluated.
 10. The methodof claim 1, wherein the optical film is a lens sheet having a pluralityof lenses formed on at least one surface, and pressed against theadhesive layer with the surface having the plurality of lenses facingthe first adhesive layer.
 11. The method of claim 10, wherein the lenssheet is a lenticular sheet having a plurality of semi-cylindricallenticules extended in parallel with one another, and the lenticularsheet is pressed against the first adhesive layer with a force appliedin a direction of an extension of the lenticules with the surface havingthe plurality of lenticules facing the first adhesive layer.
 12. Themethod of claim 1, wherein the optical film is a prism sheet having aplurality of prisms.
 13. A laminate film comprising: a transparentsupport having two opposing surfaces; an adhesive layer formed on one ofthe two opposing surfaces of the transparent support; and an opticalfilm bonded to the transparent support via the adhesive layer, whereinthe adhesive layer is made of a material of which the cured statechanges by an application of external energy, and the transparentsupport has a roughness Rt satisfying Rt≦2 μm when the roughness Rt isdefined as the distance between the highest crest and the deepest troughwithin a range of a length evaluated.
 14. The laminate film of claim 13,wherein the adhesive layer has a gel fraction of 50 wt % or more. 15.The laminate film of claim 13, wherein the optical film is a lens sheethaving a plurality of lenses formed on at least one surface, and pressedagainst the adhesive layer with the surface having the plurality oflenses facing the adhesive layer.
 16. The laminate film of claim 13,wherein the optical film is a prism sheet having a plurality of prisms.17. A method for fabricating a display device, the display devicecomprising a display element and an optical film placed on a viewer'sside of the display element, the method comprising the steps of:producing the display element; and bonding the optical film to a surfaceof the display element on the viewer's side via an adhesive film;wherein the adhesive film includes a transparent support having a firstadhesive layer formed on one of two opposing surfaces, the firstadhesive layer being made of a material of which the cured state changesby an application of external energy, and the step of bonding theoptical film to the surface of the display element on the viewer's sidecomprises the steps of: applying external energy to the first adhesivelayer; pressing the optical film against the first adhesive layer tostick the optical film and the first adhesive layer together; curing thefirst adhesive layer to a degree of hardness with which an adhesionstate between the optical film and the first adhesive layer is fixedwhile the optical film and the first adhesive layer are kept stucktogether; and after curing of the first adhesive layer, bonding theother of the two opposing surfaces of the transparent support and thedisplay element via a second adhesive layer.
 18. The method of claim 17,wherein the display element is a liquid crystal display elementcomprising a pair of substrates, liquid crystal material sandwichedbetween the pair of substrates, and optical characteristic changingmeans placed on at least the viewer's side of the pair of substrates forchanging the optical characteristics of incident light, and the opticalfilm is bonded to the liquid crystal display element by bonding theoptical characteristic changing means and the transparent support of theadhesive film together via the second adhesive layer.
 19. The method ofclaim 17, wherein the first adhesive layer is made of anultraviolet-curable resin.
 20. The method of claim 17, wherein the stepof curing the first adhesive layer comprises the step of leaving thefirst adhesive layer and the optical film standing while the firstadhesive layer and the optical film are kept stuck together.
 21. Themethod of claim 17, wherein the step of curing the first adhesive layercomprises the step of leaving the first adhesive layer and the opticalfilm standing while the first adhesive layer and the optical film arekept stuck together so that a gel fraction of the first adhesive layeris 50 wt % or more.
 22. The method of claim 17, wherein a surfaceprotection film is provided at least on the first adhesive layer forprotecting the first adhesive layer, the thickness t of the surfaceprotection film being in a range of 0.035 mm≦t≦0.2 mm, and the methodfurther comprises the step of peeling off the surface protection filmbefore the step of pressing the optical film against the first adhesivelayer.
 23. The method of claim 17, wherein the surface of the displayelement to be bonded with the second adhesive layer includes a regionhaving a roughness Rt1 satisfying Rt1>2 μmwhen the roughness Rt1 isdefined as the distance between the highest crest and the deepest troughwithin a range of a length evaluated.
 24. The method of claim 17,wherein the transparent support has a roughness Rt2 satisfying Rt2≦2μmwhen the roughness Rt2 is defined as the distance between the highestcrest and the deepest trough within a range of a length evaluated. 25.The method of claim 18, wherein the optical characteristic changingmeans is a polarizing plate.
 26. The method of claim 18, wherein theoptical characteristic changing means is a phase plate.
 27. The methodof claim 17, wherein the optical film is a lens sheet having a pluralityof lenses, and pressed against the first adhesive layer with the surfacehaving the plurality of lenses facing the first adhesive layer.
 28. Themethod of claim 27, wherein the lens sheet is a lenticular sheet havinga plurality of semi-cylindrical lenticules extended in parallel with oneanother, and the lenticular sheet is pressed against the first adhesivelayer with a force applied in a direction of an extension of thelenticules with the surface having the plurality of lenticules facingthe first adhesive layer.
 29. The method of claim 17, wherein theoptical film is a prism sheet having a plurality of prisms.
 30. A methodfor fabricating a display device, the display device comprising adisplay element and a lens sheet placed on the viewer's side of thedisplay element, the lens sheet having a plurality of lenticulesextended in parallel with one another, the method comprising the stepsof: producing the display element; forming an adhesive layer on theviewer's side of the display element; placing the lens sheet so that thesurfaces of the lenticules face the adhesive layer; and pressing thelens sheet against the adhesive layer by applying a force in a directionof an extension of the lenticules.